bug: irch for rch and evt packages

[jdhughes-usgs]

Describe the bug
flopy cannot load existing models https://github.com/MODFLOW-USGS/modflow6-testmodels/tree/master/mf6/test001h_evt_array4 and
https://github.com/MODFLOW-USGS/modflow6-testmodels/tree/master/mf6/test001h_rch_array4. This is a recent issue that crept in sometime recently.

To Reproduce
Steps to reproduce the behavior:

1. Download the two models
2. Load with sim = flopy.mf6.MFSimulation.load(sim_ws=".")
3. Results in error MFDataException: An error occurred in data element "irch" model "gwf6" package "rcha". The error occurred while setting data in the "_set_data" method.

Expected behavior
Load the models without an error.

Screenshots
None.

Desktop (please complete the following information):

• OS: MacOS, Linux, Windows

[wpbonelli]

confirmed models now load without error after #2146